Aluminium soldering composition

ABSTRACT

There is described a composition for soft soldering aluminium or alloys thereof using a fluxed solder composition. The fluxed solder composition comprises a soldering flux suitable for use in soft soldering aluminium and its alloys and a soft solder alloy of lead, tin and silver and, optionally, up to 3% copper.

BACKGROUND OF THE INVENTION

This invention relates to the soldering of aluminium of aluminium alloysand, more particularly, is concerned with a method of solderingaluminium or aluminium alloys using fluxed solder compositions, and withfluxed solder compositions for use in said method.

There have been proposed a number of solder alloys which are said to besuitable for soldering a member made of aluminium or of an aluminiumalloy to another member which latter member may or may not be ofaluminium or of an aluminium alloy. These known solder alloys includethe so-called "soft solders", which are solders melting below 350° C.The soft solders are generally preferable to the higher melting point"hard solders", and to the "brazing" and "welding" alloys, for any typeof joint incorporating a member of aluminium or of an aluminium alloysince with soft solders the expansion, changes of temper and distortionof the member which may take place are less severe at lowertemperatures. The use of soft solders also reduces the energy and timerequired to make a joint, bearing in mind that for aluminium the amountsof energy and time required increase rapidly with soldering temperaturesince aluminium has a relatively high specific heat. Furthermore, thelower the melting range of the solder used, the wider is the choice ofsuitable flux compositions which do not char during soldering. The lowmelting point of a soft solder also permits it to be used onheat-sensitive components such as those found in the electronics andelectrical industries.

There are a wide range of metals which are generally recognized by thoseskilled in the art as being susceptible to soft soldering processes.Such metals include plain carbon steels, brass and copper alloys ingeneral, and nickel alloys. With an appropriate soldering flux,stainless steels can also be soft soldered. Metals such as tungsten,titanium, molybdenum and chromium cannot usually be soft soldered.

Further information concerning the soft soldering of aluminium can befound in

I. Aluminum Soldering Handbook published by the Aluminum Association inNew York in 1971

And in

Ii. Soldering Aluminium published by the Aluminium Federation in Londonin 1968.

There are however two disadvantages which may arise from the use of thesoft solders heretofore used for soldering aluminium or alloys ofaluminium. Firstly, the corrosion resistance of joints made with most ofthese soft solders is not always satisfactory; failure tends to takeplace along the interface between the soft solder alloy and thealuminium member so that the electrical and/or mechanical connectionacross the joint may be lost. Secondly, these soft solder alloys oftencontain one or more elements (such as bismuth, zinc, cadmium orantimony) which are incompatible with certain other metals, alloys,solders or platings which may form one or more of the other members of ajoint comprising an aluminium or aluminium alloy member. For example,antimony attacks zinc in brass, while bismuth, zinc and cadmium areliable to mix with any tin/lead solder which is present to produce amixed alloy joint of unacceptable composition. National andInternational specifications for such soldered joints strictly prohibitmore than incidental quantities of such elements. Furthermore, softsolder alloys containing one or more of bismuth, zinc, cadmium orantimony may not be ductile enough for production in large quantity inthe form of thin solder wire or flux-cored solder wire, may not flow onand wet other members of different metals sufficiently well, and mayreduce the corrosion resistance of the joint.

It is an object of the present invention to provide a fluxed soft soldercomposition suitable for soldering a member of aluminium or of analuminium alloy to another metallic member, which soft soldercomposition has a melting point less than 300° C and can provide asoldered joint with substantial corrosion resistance.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided afluxed solder composition suitable for soldering a member of aluminiumor of an aluminium alloy to another metallic member, which fluxed soldercomposition comprises a flux suitable for use in aluminium soldering anda soft solder alloy, having a melting point of less than 300° C,comprising at least 35% by weight lead, at least 10% by weight tin andx% by weight silver, where x = 0.1 + (5 × 10⁻⁴)(Sn)² + (1 × 10⁻⁵)(Sn)³,where (Sn) is the percentage by weight of tin in the soft solder alloyand, optionally, up to 3% by weight copper, the balance, if any,consisting of incidental elements and impurities.

According to a second aspect of the present invention there is provideda method of joining a first member made of aluminium or of an aluminiumalloy to a second metallic member at a joint site, the method comprisingthe steps of (a) disposing said first and second members in the positionin which they are to be jointed, (b) providing at said joint site afluxed solder composition according to the first aspect of theinvention, and (c) soldering together said first and second members.

In the soft solder alloys used in the compositions according to thefirst aspect of the invention, the minimum quantity of silver in thealloy is determined by the amount of tin present. The Applicants havefound that such a requirement is essential if the range of compositionof the alloys of the invention is not to include some alloys ofunsatisfactory corrosion resistance.

DETAILED DESCRIPTION OF THE INVENTION

Fluxed solder compositions and, in particular, flux-cored soldercompositions are known. Fluxed solder compositions permit theintroduction of both flux and alloy to the area of the joint siteco-operatively and simultaneously and in constant proportions of flux tosolder. They are commonly formed of a solder alloy and have associatedtherewith a quantity of a soldering flux, the arrangement being suchthat when the fluxed solder composition is applied to the joint site inthe soldering process, the flux associated therewith flows progressivelyonto the joint site as the solder alloy of the fluxed solder compositionis consumed, i.e. melted and solidified during the process. The fluxedsolder composition is conveniently provided as an elongate member havinga substantially uninterrupted core, or plurality of separate cores, ofthe flux, which core or cores extend longitudinally through the interior(as distinct from the surface) of the solder alloy. Fluxed soldercompositions of this convenient form are herein referred to asflux-cored solder compositions. However, it should be understood that afluxed solder composition can be constituted by an elongate member ofthe solder alloy coated with a quantity of the soldering flux or by anintimate mixture of a flux and a solder powder, the mixture being, forexample, a dimensionally stable solid or even a paste or cream in therange of normal room temperatures. Flux-cored solder compositions may bemade by extruding the solder alloy so as to form an elongate wire rodwhile simultaneously introducing flux cores into cavities in the wire orrod. The diameter of the extruded wire or rod may then be reduced by,for example, rolling or drawing.

Where reference is made herein to the melting point of an alloy, thisshould be understood to refer to the liquidus temperature of that alloy.The proportions of the elements contained in the soft solder alloy areexpressed in this specification as percentages by weight of the alloy.

The soft solder alloy used in the invention contains at least 10% tinfor a number of reasons. Firstly, such alloys are more easily drawn intoflux-cored wires than are alloys having less than 10% tin. Furthermore,alloys with less than 10% tin have higher melting points which (i)increase the cost and difficulty of any preheating before soldering and(ii) increase the risk of overheating of heat-sensitive devices near thejoint site. The ability of tin-lead solder alloys to wet and spread overaluminium surfaces is improved with tin contents over 10%.

An addition of up to 3% copper to the soft solder alloy may be useful toimprove the strength and creep resistance of the solder alloy.

The fluxed solder conposition of this invention may be a flux-coredsolder member in the form of a stick, or a wire or ribbon which may beconveniently stored in coil form with or without a former. The fluxedsolder composition may also be in the form of a particular shapeselected for a special purpose and stamped or cut from a stick, wire orribbon.

Conveniently, the requisite quantity of flux is incorporated in thesolder alloy as one, or preferably as a plurality of, substantiallycontinuous strands of flux extending longitudinally through the interiorof the solder alloy. The fluxed solder composition of the invention mayalso take the form of a mixture of solder alloy powder and flux, with orwithout an additional carrier, and the mixture may take the form of, forexample, a dimensionally-stable solid or a cream or paste.

Fluxes suitable for the soldering of aluminium and for inclusion influxed solder compositions according to the invention will generally bean organic flux of the type comprising (a) certain amines (e.g.diethylenetriamine) and (b) either fluoboric acid and/or certain saltsof fluoboric acid, (e.g. ammonium fluoborate and zine fluoborate) orcertain alkali metal and/or ammonium halides (e.g. lithium chloride,ammonium chloride and sodium fluoride) and, optionally, (c) certainoxides, (e.g. zine oxide or cadmium oxide); or a reaction flux of thetype comprising (a) certain heavy metal chlorides, (e.g. stannouschloride and zinc chloride) and at least one of (b) certain alkali metaland/or ammonium halides (e.g. lithium chloride, aluminium chloride andsodium fluoride) and (c) certain reducing and/or wetting agents (e.g.hydrazine hydrochloride and oleic acid); or a mixture of an organic fluxand a reaction flux.

In general, the organic flux will comprise from 20 to 80 parts by weightof amine(s), from 5 to 60 parts by weight of fluoboric acid and/orsalt(s) thereof and optionally up to 15 parts by weight of metaloxide(s). The reaction flux will in general comprise from 50 to 90 partsby weight of heavy metal chloride(s) and optionally up to 50 parts byweight of alkali metal and/or ammonium halide(s) and/or up to 10 partsby weight of reducing and/or wetting agent(s).

Such aluminium soldering fluxes may be conveniently prepared in liquidform by diluting them in or suspending them in a suitable solvent (whichmay in some cases be water or an alcohol) in appropriate concentrations.Alternatively, the fluxes may be in solid form.

In order to test the corrosion resistance of a number of soldered jointsmade from various soft solder alloys, the investigations detailed belowwere undertaken. In the following description, reference will be made tothe accompanying drawings in which:

FIG. 1 shows a perspective view of a "T-piece" test specimen; and

FIG. 2 is a graph of the variation of the corrosion resistance ofvarious joints formed with soft solder alloys according to the tin andsilver content of the soft solder alloy used to form the joint.

Referring to FIG. 1, a number of soft solder alloys 1 were employed toform soldered joints between the horizontal and vertical members 3 and 2respectively of "T-piece" test specimens where at least one of the twomembers was either aluminium of an aluminium alloy. The nominalcompositions of the aluminium alloys used in these "T-pieces" are setout in Table 1. In Table 1 the designations S1C, N4, N8, H9, H15 and H30refer to aluminium alloys described in British Standard No. 1470, whilethe numbers 3003, 5052 and 6061 are U.S. AA standard aluminium alloys.Either four or six similar "T-piece" test specimens were prepared foreach combination of aluminium or aluminium alloy and solder alloyrecorded in Table 1. An organic flux of the type described above wasused in the soldering process. The soldered joints were tested forresistance to electrolytic corrosion as follows. Of each set of foursimilar specimens, two were stored in normal office ambient conditionsand two were stored by immersion in a standard synthetic brine solutionat ambient temperature. The standard synthetic brine solution isdescribed in British Standard No. 2011; Part 2K: 1963 and has thecomposition:

Sodium chloride -- 27 g

Anhydrous magnesium chloride -- 6 g

Anhydrous calcium chloride -- 1 g

Potassium chloride -- 1 g

Distilled water to form 1 liter

The specimens were not subjected to any externally applied stress duringthe test. When six similar test specimens were available, four weretreated as described above and the remaining two specimens were storedin a Long Term Damp Heat test enclosure (40 ± 2° C, 90-95% R.H.according to British Standard No. 2011, part 2C).

It is usual in practical soldering to remove deliquescent flux residuesimmediately after soldering by washing the soldering joints in water. Inorder to reproduce the conditions of practical soldering as far as isconsistent with a simple accelerated corrosion test, the freshlysoldered test pieces were, unless stated, all washed in cold waterbefore being introduced into the test conditions. It was also consideredthat the washing step served to make the test results more reproducibleby reducing the possibility of (a) changes in electrolyte compositiondue to the presence of spurious ionic species originating from the fluxresidues and (b) reaction between the brine solution and the fluxresidues at the joint site which might change the initial concentrationof brine salts at the joint site. The joints were visually examinedperiodically, and a failure noted when the two members lost mechanicalcontact and parted under their own weight or upon applying lightpressure with a probe.

Blank spaces in the Tables indicate that the joints did not fail duringthe test which, when the data given in the Tables were recorded, hadbeen in progress for 450 days in the case of Table 2, 400 days in thecase of Table 3, 300 days in the case of Table 4 and 200 days in thecase of Table 5. Office storage was used as a control condition, to showwhether failure of a particular solder composition was due to someintrinsic weakness or to the effects of the environment. The resultsrecorded in Tables 2, 3 and 4 for joints between aluminium S1C anditself and, in Table 2, between aluminium S1C and copper, show thatunder normal office storage conditions there is no catastrophicintrinsic weakening of the joint at ambient temperature, whatever thecomposition of the solder alloy used. The results given in Table 2 showthat Long Term Damp Heat gives a pattern of joint endurance similar tothat produced by brine immersion, though it is extended over a longertime period. The brine test therefore seemed to be a satisfactoryaccelerated corrosion test and subsequently the Long Term Damp Heat testwas omitted and no results therefor are given in Tables 3 and 4. Thespecimens were tested in duplicate in both brine and under officestorage conditions.

Tables 2 and 3 give the endurance of joints made with various tin-lead,lead-silver and tin-lead-silver solder alloys. The results aresummarised in FIG. 2 from which it can be seen that those lead-silverand tin-lead-silver solders having compositions in the area above uppercurve AA' usually retained their strength for long periods (over 200days) of brine immersion. The tin-lead solders and tin-lead-silversolders having compositions in the area below lower curve BB' (whichcurve is represented by the expression (Ag) = 0.1 + (5 × 10⁻⁴)(Sn²) + (1× 10⁻⁵)(Sn³) where (Ag) and (Sn) are the percentages by weight of silverand tin respectively in the soft solder alloy) generally lost theirstrength completely within a comparatively short period (rarely morethan 25 days) of brine immersion. Joints made of tin-lead-silver solderswhose composition falls between upper and lower curves AA' and BB'respectively had intermediate, variable or uncertain endurance. Ingeneral, therefore, it is advisable to select the composition of thesolder alloy to be inside the region above the upper curve AA' forsatisfactory resistance of the soldered joint to this electrolyticcorrosion test.

Immersion in 3% sodium chloride solution for 90 days has beenrecommended as a corrosion test; (ss Y. Sugiyama and H. Irie, "Corrosionresistance of soldered joints in aluminium", Sumitomo Light MetalTechnical Reports 1967, 8 (4), 23). It will be noted that the solderalloys tested in these investigations and having compositions above theupper curve AA' for the most part exceed this performance.

By way of example, in order that the soldered joint should havereasonable resistance to corrosion, the composition of the solder alloyshould be such that the tin content does not exceed 18% if the silvercontent is 0.5%, the tin content should not exceed 25% if the silvercontent is 1%, the tin content should not exceed 35% if the silvercontent is 2%, the tin content should not exceed 45% if the silvercontent is 4% and the tin content should not exceed 60% if the silvercontent is 7%.

Table 4 shows the effect of electrolytic corrosion resistance in brine,of adding certain other metallic alloy components to an 18 tin- 80 lead-2 silver solder alloy. It illustrates the very marked reduction incorrosion resistance of this solder alloy when significant quantities ofbismuth, cadmium, antimony or zinc are present, but shows no such losswhen 1% copper is present.

In a further series of tests there were formed organic-fluxed soldercompositions, one of which comprised a tin-lead soft solder alloy andone of which comprised a tin-lead-silver solder alloy. The fluxed soldercompositions were used to solder members of aluminium or aluminium alloyto other members of aluminium, one of its alloys or another metal. Thesoldered joints so formed were tested for corrosion resistance byimmersing them in a synthetic brine solution as described above. For oneset of test specimens such immersion was effected without first removingany flux residues from the vicinity of the soldered joints and foranother set of joints flux residues were removed before immersion. Theresults, in Table 5, tend to suggest that the presence of organic fluxresidues has little effect on the corrosion resistance of the solderedjoints.

Table 5 gives the results of a comparison between joints made with 30tin- 70 lead and 24 tin- 2 silver- 74 lead solders, (solder alloys 32and 43 respectively), the joint members being chosen from particularaluminium alloys and from other metals as shown. It is apparent from theresults shown in Table 5 that the silver-bearing solder alloy 43provides greater corrosion resistance than the tin-lead alloy 32.However, the improvement was much less marked where one of the jointmembers is of N8 or H15 alloy, particularly when the other joint memberis not itself an aluminium alloy.

                                      TABLE 1                                     __________________________________________________________________________    COMPOSITIONS OF ALUMINIUM ALLOYS                                              Designation                                            Additional             of                                                     restraints on          Alloy  Aluminium                                                                            Copper                                                                             Magnesium                                                                           Silicon                                                                            Iron                                                                              Manganese                                                                           Zinc                                                                              Titanium                                                                           Chromium                                                                            composition.           __________________________________________________________________________    SIC    99.0 minimum                                                                         0.10 --    0.5  0.7 0.1   0.1 --   --    Cu+Si+Fe+                                                                      Mn+Zn=1               3003   rem.   0.20 --    0.6  0.7 1.0 to 1.5                                                                          0.10                                                                              --   --                           5052   rem.   0.10 2.2 - 2.8                                                                           (Si + Fe=0.45)                                                                         0.10  0.20                                                                              --   0.15-0.35                    6061   rem.   0.15-0.40                                                                          0.8 - 1.2                                                                           0.40-0.8                                                                           0.7 0.15  0.25                                                                               0.15                                                                              0.15-0.35                    N4     rem.   0.10 1.7 - 2.4                                                                           0.5  0.5 0.5   0.2 0.2  0.25  Mn+Cr=0.5              N8     rem.   0.10 4.0 - 4.9                                                                           0.40 0.40                                                                              0.5 - 1.0                                                                           0.2 0.2  0.25                         H9     rem.   0.10 0.4 - 0.9                                                                           0.3-0.7                                                                            0.40                                                                              0.10  0.2 0.2  0.10                         H15    rem.   3.9 -5.0                                                                           0.2 - 0.8                                                                           0.5-1.0                                                                            0.7 0.4 - 1.2                                                                           0.2 0.2  0.10                         H30    rem.   0.10 0.5 - 1.2                                                                           0.7-1.3                                                                            0.5 0.40-1.0                                                                            0.2 0.2  0.25                         The figures are given in wt% and are maxima unless otherwise                  __________________________________________________________________________    indicated.                                                                

                                      TABLE 2                                     __________________________________________________________________________    COMPARISON OF TIN-LEAD AND TIN-LEAD-SILVER SOLDER ALLOYS                                      Days to failure of soldered "T-joint" test specimen                           between                                                                       a commercial grade aluminium (SIC) horizontal member and      Composition of  either a commercial grade aluminium (SIC) or a copper         Solder Alloys   vertical member.                                              Reference       OFFICE STORAGE                                                                           LONG TERM DAMP HEAT BRINE IMMERSION                of Alloy                                                                            Sn  Pb Ag Aluminium                                                                           Copper                                                                             Aluminium Copper    Aluminium                                                                              Copper                __________________________________________________________________________    1     100 -- --            107  40   107  40   4    4   4   4                 2     60  40 --            40   40   107  107  19   7   19  7                 3     40  60 --            40   40   40   40   19   11  19  19                4     15  85 --            39   39   39   39   4    4   19  6                 5     5   95 --            18   39   39   39   4    4   4   4                 6     --  97.5                                                                             2.5                                                              7     1.0 97.5                                                                             1.5                                                              8     96.5                                                                              -- 3.5           40   40   40   40   4    4   19  6                 9     62  36 2             40   40   40   40   15   19  19  8                 10    39  60 1                  40   40   107  40   11  40  40                11    14  85 1                                                                12    5   93.5                                                                             1.5                                                              13    39.9                                                                              60 0.1           40   40   40   40   19   19  40  40                14    39.5                                                                              60 0.5           40   40   40   40   40   19  19  19                15    38  60 2             40   40             40   40  40  82                __________________________________________________________________________

                  TABLE 3                                                         ______________________________________                                        COMPARISON OF TIN-LEAD AND                                                    TIN-LEAD-SILVER SOLDER ALLOYS                                                                Days to failure of soldered "T-joint"                                         test specimens between horizontal and                          Composition of vertical members of a commercial                               Solder Alloys  grade aluminium (SIC)                                          Reference                                                                     of Alloy                                                                              Sn     Pb    Ag  Office Storage                                                                           Brine Immersion                           ______________________________________                                        04      15     85    --             11/2   11/2                               16      14.5   85    0.5                   217                                11      14     85    1                                                        17      13     85    2              277                                       31      20     80    --             61/2   61/2                               19      19.5   80    0.5            61/2   61/2                               20      19     80    1                     32                                 21      18     80    2                                                        32      30     70    --             11/2    4                                 23      29.5   70    0.5            61/2   61/2                               24      29     70    1              61/2   29                                 25      28     70    2                     217                                26      60     37    3              61/2   61/2                               27      46     50    4              28     30                                 28      56     37    7                                                        29      34     61    5              234                                       ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        COMPARISON OF TIN-LEAD, TIN-ZINC,                                             and TIN-LEAD-SILVER SOLDER ALLOYS                                             WITH TIN-LEAD-SILVER ALLOYS                                                   HAVING VARIOUS ADDITIONAL ELEMENTS                                            Days to failure of soldered "T-joint" test specimens                          between horizontal and vertical members                                       of a commercial grade aluminium (SIC)                                         Refer-                                                                        ence of                           Office Brine                                Alloy  Sn    Pb     Ag  Others    Storage                                                                              Immersion                            ______________________________________                                        21     18    80     2                                                         25     28    70     2                    109                                  30     30    68     --   2 Cd            4    4                               31     20    80                   4      4                                    32     30    70                          4    4                               33     18    70     2   10 Bi            11   68                              34     18    70     2   10 Cd            109  4                               35     18    79     2    1 Cu                 221                             36     18    78     2    2 Sb     0      4    0                               37     18    70     2   10 Zn            4    4                               38     18    74.25  2   2.5 Cd, 0.25 Cu, 20   109                                                     0.5 Sb, 2.5 Zn                                        39     90    --     --  10 Zn            20   126                             40     80    --     --  20 Zn            4    4                               41     70    --     --  30 Zn            20   11                              ______________________________________                                    

                                      TABLE 5                                     __________________________________________________________________________    COMPARISON OF SOLDER ALLOY 32 (30 Sn 70 Pb) AND SOLDER ALLOY 43               (24 Sn 74 Pb 2 Ag) ON VARIOUS JOINT-MEMBER ALLOYS                             For each type of horizontal joint member, the upper line of results           refers to                                                                     joints frim which flux residue had been removed before immersion in the       brine. The                                                                    lower line of results relates to joints from which the flux residue had       not been                                                                      removed before immersion.                                                     Days to failure during brine immersion, of soldered "T-joint" test            specimens                                                                     Designation                                                                   of vertical                     Stainless                                     member  Cu    Brass Ni    Steel Steel N8  H9                                  Designation                                                                   of horizont-                                                                  al member                                                                             43 32 43 32 43 32 43 32 43 32 43                                                                              32                                                                              43                                                                              32                                __________________________________________________________________________               41/2  41/2                                                                             115                                                                              41/2                                                                             132                                                                              11/2  11/2                                       N4                                                                                       41/2  11/2                                                                             57 41/2                                                                             152                                                                              41/2  41/2                                               19 11/2                                                                             19 11/2                                                                             41/2                                                                             11/2                                                                             19 11/2                                                                             19 11/2                                                                             57                                                                              41/2                                                                            33                                                                              11/2                              N8                                                                                    19 11/2                                                                             19 11/2                                                                             19 11/2                                                                             26 11/2                                                                             19 11/2                                                                             19                                                                              11/2                                                                            26                                                                              11/2                                      115                                                                           40 11/2                                                                             17 11/2                                                                             132                                                                              11/2                                                                             152                                                                              41/2                                                                             37 7        11/2                              H9                                                                                    0  11/2                                                                             132                                                                              41/2                                                                             170                                                                              41/2                                                                             170                                                                              41/2                                                                             26 11/2   26                                                                              11/2                                                        115                                                         26 41/2                                                                             19 11/2                                                                             19 41/2                                                                             26 7  35 7                                          H15                                                                                   19 11/2                                                                             19 11/2                                                                             19 41/2                                                                             19 11/2                                                                             26 41/2                                                                 132                                                         17 11/2  11/2                                                                             17 11/2                                                                             40 11/2                                                                             33 11/2                                       H30                                                                                   17 11/2  11/2                                                                             115                                                                              11/2                                                                             40 11/2                                                                             115                                                                              11/2                                               41/2  41/2                                                                             26 41/2                                                                             115                                                                              11/2  41/2                                          SIC                                                                                      41/2  7  150                                                                              41/2                                                                             170                                                                              41/2  41/2                                       Designation                                                                   of vertical                                                                   member  H15   H30   SIC   3003  5052  6061                                    Designation                                                                   of horizont-                                                                  al member                                                                             43 32 43 32 43 32 43 32 43 32 43  32                                  __________________________________________________________________________                           11/2                                                   N4                                                                                                115                                                                              11/2                                                                          57                                                             19 11/2                                                                             37 11/2                                                                             17 11/2                                                                             40 11/2                                                                             132                                                                              11/2                                                                             19  11/2                                N8                                                                                    19 11/2                                                                             19 11/2                                                                             33 11/2                                                                             40 11/2                                                                             26 11/2                                                                             19  11/2                                        63 11/2  11/2                                                                             183                                                                              11/2                                                                             40 11/2                                                                             176                                                                              11/2   11/2                                H9                                                                                    33 11/2                                                                             152                                                                              11/2  11/2                                                                             40 11/2                                                                             132                                                                              11/2                                                                             176 11/2                                        63 7  57 7  132                                                                              7  132                                                                              11/2                                                                             47 19 115 19                                  H15                                                                                   33 7  152                                                                              26 115                                                                              7  176                                                                              19 115                                                                              7  152 7                                                             132                                                               154                                                                              11/2  11/2                                                                             40 11/2  11/2                                                                             176 11/2                                H30                                                                                         57 11/2                                                                             115                                                                              11/2                                                                             40 11/2                                                                             115                                                                              11/2                                                                             57  11/2                                SIC                    7     41/2  11/2   11/2                                                       11/2  41/2  11/2   11/2                                __________________________________________________________________________

We claim:
 1. A fluxed solder composition for use in soft solderingaluminium or aluminium alloys, said composition comprising inassociation (a) a soft solder alloy having a melting point of less than300° C, said alloy consisting essentially of at least 35% by weight oflead, not less than 10% by weight of tin, from 0 to 3% by weight ofcopper, and silver with the relative amounts of silver and tin in saidalloy being such that said amounts of silver and tin are within the areaabove the curve AA' in FIG. 2 of the drawings, and (b) a flux suitablefor use in aluminium soldering selected from organic fluxes and reactionfluxes.
 2. A fluxed solder composition as claimed in claim 1, whereinthe fluxed solder composition is in the form of a flux cored soldermember.
 3. A fluxed solder composition as claimed in claim 1, comprisinga mixture of the flux and a plurality of discrete particles of the softsolder alloy.
 4. A fluxed solder composition as claimed in claim 3,wherein the composition of the mixture is such that the mixture isdimensionally stable at room temperature.
 5. A fluxed solder compositionas claimed in claim 1, wherein said organic flux comprises:a. an amine,and b. a member selected from the group consisting of fluoboric acid,salts of fluoboric acid, alkali metal halides, and ammonium halides; andsaid reaction flux comprises: a heavy metal chloride.
 6. A fluxed soldercomposition as claimed in claim 5, wherein said organic flux furthercomprises a metal oxide.
 7. A fluxed solder composition as claimed inclaim 5, wherein said amine is diethylenetriamine, said salts offluoboric acid are ammonium fluoborate and zinc fluoborate, said alkalimetal halides are lithium chloride and sodium fluoride, said ammoniumhalide is ammonium chloride, and said heavy metal chloride is selectedfrom the group consisting of stannous chloride and zinc chloride.
 8. Afluxed solder composition as claimed in claim 6, wherein said metaloxide is selected from the group consisting of zinc oxide and cadmiumoxide.
 9. A fluxed solder composition as claimed in claim 5, whereinsaid reaction flux further comprises at least one member selected fromthe group consisting of alkali metal halides and ammonium halides.
 10. Afluxed solder composition as claimed in claim 9, wherein said alkalimetal halides are lithium chloride and sodium fluoride and said ammoniumhalide is ammonium chloride.
 11. A fluxed solder composition as claimedin claim 5, wherein said reaction flux further comprises at least onemember selected from the group consisting of reducing agents and wettingagents.
 12. A fluxed solder composition as claimed in claim 11, whereinsaid reducing agent is hydrazine hydrochloride and said wetting agent isoleic acid.